Wednesday 11 June 2008 19.01 EDT
First published on Wednesday 11 June 2008 19.01 EDT

Britain's largest environment groups have strongly rejected plans for a massive £15bn tidal barrage across the Severn that would provide about 5% of the UK's annual electricity demand and help the government meet climate-change targets.

In the first shots of what is expected to become one of the fiercest environmental battles in years, the groups, which include the National Trust, the RSPB and WWF, but not Greenpeace, have challenged the government to find cheaper and less destructive ways of generating renewable electricity from the estuary.

Britain will need to generate nearly 40% of its electricity from renewable resources by 2020 to meet its EU targets, and a 10-mile long tidal barrage with 200 turbines between Cardiff and Weston-super-Mare is widely seen in government as one of the most attractive options. Plans for a barrage have been proposed for more than 100 years.

But the coalition of 10 groups, with a membership of more than 5 million people, says a barrage would be economically dubious and ecologically disastrous. It would, the coalition says, destroy nearly 86,486 acres (35,000 ha) of highly protected wetlands across the estuary. More power could be generated more cheaply by using other green technologies, the group says.

Their report, commissioned from the economics consultancy Frontier Economics, follows a study last year by the government's environmental advisers, the Sustainable Development Commission (SDC).

The commission found in favour of a barrage on condition that it be state funded and that the lost wetlands be compensated for elsewhere. The government is now doing its own feasibility studies.

The report challenges the idea that tidal energy from the Severn would be best for Britain. "The cycle of the tides in the Severn means that a barrage would not necessarily provide electricity at peak times."

It also suggests 5m tonnes of CO2 will be emitted during construction and another 5m tonnes emitted during transport of the materials - undermining claims that the barrage would help reduce emissions.

The group says that the real cost could be much higher than the widely quoted £15bn. "This does not take into account costs of land acquisition in Cardiff and Weston or the creation of new wildlife habitats to compensate for the lost land."

The coalition also rejects the SDC condition that the barrage be built and run by the state as it would be of such national importance. This, says the report's author, Matthew Bell, would not be permitted under Treasury rules, and would not, anyway, warrant special government subsidies or other forms of public investment. Bell said: "It is hard to think of reasons for the public sector to build or operate a barrage which would not be equally applicable to many other projects and assets that sit in the private sector. Not only is the private sector more than able to finance a scheme of this scale but, even using the most conservative estimates of costs, the barrage is one of the most expensive options for clean energy generation there is."

Graham Wynne, chief executive of the RSPB, said: "There are good reasons for trying to harness the energy potential of the Severn estuary. But the estuary is truly exceptional for its ecological value. The [SDC] has already confirmed that a barrage would fundamentally change the nature of the estuary. Frontier's report shows that this exorbitantly expensive and massively damaging proposal cannot be justified on economic grounds - there are simply too many cheaper options for clean energy generation."

Tony Burton, strategy director at the National Trust, said: "The Severn estuary is a unique and valuable asset, rich in wildlife and striking landscapes. While we support strong action to tackle climate change, we need to do this in a cost-effective way and respect the importance of our natural environment. This study demonstrates that the government should consider other ways of meeting our renewable targets which make better use of public money and are at less cost to the environment."

The land that would be submerged hosts about 68,000 birds in winter, including huge flocks of dunlins and shelducks, together with Bewick's swans, curlews, pintails, wigeons and redshanks. Breeding birds feeding on the estuary in summer include curlews, shelducks and oystercatchers. At least 30,000 salmon and tens of thousands of shads, lampreys and sea trout use the estuary to reach spawning grounds in the Usk and Wye rivers. Eels swim back down these rivers to reach spawning grounds at sea and millions of elvers return in the spring.